Swine flu shook the public health world in part because, when it surfaced, it behaved differently than other strains. Instead of seeing hospitalizations mostly among the young and old, healthy adults between ages 25 and 49 proved especially vulnerable, said Bolton.
This year, 43 percent of the season's 44 hospitalizations are among this age group, according to Utah's latest influenza report.
So far this year H1N1 isn't making quite the same splash, however.
Flu activity started about a month early this year, in November, but it is now closely tracking last year's rate, which was higher than average but not as high as in 2009, said Bolton. "There is a level of communitywide immunity to [H1N1]. In 2009, no one had encountered it before so pretty much everyone was susceptible."
This year's vaccine covers swine flu along with other common strains.
It's not too late to get immunized, and there's ample supply of the vaccine, but the sooner the better, say health officials, stressing it takes two weeks to develop full immunity.
Area hospitals, including Intermountain Healthcare facilities, have put visitor restrictions in place to reduce exposure for vulnerable patients.
This includes barring child visitors, those under age 14, to newborn intensive-care units, said Jess Gomez, a spokesman at Intermountain Medical Center.
"We're asking people to take precautions and use common sense," he said. "Wash your hands and if you're sick, don't come. And if you think you might be getting sick, use a mask."
Unlike many viral respiratory infections, such as the common cold, the flu can cause severe illness and life-threatening complications, according to the U.S. Centers for Disease Control and Prevention (CDC).
Each year 5 percent to 20 percent of the population gets the flu and more than 200,000 are hospitalized. It is a leading cause of death, killing between 3,000 and 49,000 people annually, estimates the CDC.
Last year five children in Utah died from the flu, more than usual, said Bolton. "We usually see between one and three deaths a year."